Mechanical plating



United States Patent 3,479,209 MECHANICAL PLATING Erith T. Clayton, Baltimore, Md., assignor to Peen Plate, Inc., Baltimore, Md., a corporation of Maryland No Drawing. Filed July 22, 1966, Ser. No. 567,087

Int. Cl. C23c 3/02 US. Cl. 117109 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of mechanically plating objects and to materials used in such methods. More particularly, the invention relates to improvements in the mechanical plating process and materials described in US. Patents No. Re. 23,861; No. 2,689,808; No. 2,- 640,002; No. 3,023,127; and No. 3,132,043. In the mentioned patents is disclosed a method of applying metallic coatings to metallic objects by subjecting finely divided metallic particles to mechanical energy in an aqueous medium to flatten and cold weld the particles to the metallic object to thereby build up a continuous, adherent metallic coating on the metal object.

This process is in widespread industrial use, but due to the variety and complexity of parts to be plated some of the problems created are difficult to solve. It usually happens that a manufacturer plates at wide variety of parts. Even if he does not do so, there may be a wide variety of sizes for any given part. If the mechanical plating process is to compete successfully with established methods of coating, it should be able to deal successfully with all items made by any manufacturer. It is not sufficient to be able to plate, say 95 percent of the articles, because the manufacturer does not want to install a separate electroplate system, for example, to do the small percentage of his total manufacturing operations which cannot be handled by mechanical plating.

These difficulties arise from the variety of shapes and sizes which develop different tumbling characteristics when agitated in a barrel. The easiest way of explaining some of the difficulties which are encountered in practice may be to take certain individual articles and illustrate the problems which may be involved in plating them.

The simplest articles which could be encountered are probably nails. Nails are manufactured in a wide variety of sizes. There are stilt 60d spikes, long narrow box nails, large-headed roofing nails, small tacks, and then a wide variety of special nails, such as twisted Ardox nails, grooved nails, and so on. Nails are handled in large volume, and the plating barrel to handle commercial loads may range in size from 3 feet to 5 feet in diameter, for example. A 5-foot diameter barrel may carry a load of two tons of nails. The operation may work admirably with small roofing nails, for example, but not when the charge is switched to 16d box (these are long, very thin nails which bend very easily). It is known that there are active and relatively inactive zones in a tumbling barrel. Most of the work is done in the slide or descending column of material sliding down the face of the charge. Sixteen penny box nails (which may protrude into the slide) can very readily bebowed or bent. Any alteration from a straight shank is undesirable and only a limited amount of bowing can be tolerated by the nail 3,479,209 Patented Nov. 18, 1969 manufacturer. Considering another case, 60d spikes, these are thick, strong nails, which are not subject to bending or bowing in the ordinary course of events. However, these long nails do not tumble very nicely. They are usually packed in boxes arranged parallel to one another, and if the box is emptied the tangle of nails which results in a good illustration of what happens in the tumbling operation. The nails do not ride separately, but tend to revolve in a tumbled mass. This condition results in a rough and uneven plating and may result in bare areas under the heads of the nails. Now it is true that 60d nails or 16d box nails, for example may constitute only a small portion of the production of a large nail mill; nevertheless, the manufacturer would desire to have all of his nails coated by a single process and not have to maintain two separate operations to coat his nails.

Another very simple case is the plating of chains. Chains also come in a wide variety of shapes and sizes. Dealing with massive proof-coil chain, glass beads (which are normal impact material) are caught between the hammer and anvil action of one chain link striking another, and the glass beads can be ground to glass powder. A wide variety of chain sold industrially is called woven chain, and is made from wire which is bent on the links. These links constitute a widely diverse condition of shielded shapes. A good example of shielded areas in chains is the sash chain. This is made of small, fiat strips of metal bent over to form individual links. The interior surfaces of these links are extremely difficult to reach with any effective impact material. They are, moveover, so small that it is very difficult to generate energy to compact the coating onto the interior surfaces. A chain manufacturer may also manufacture, for example, snaps such as the snap on the end of a chain used for holding dogs. Obviously, the tumbling characteristics of long lengths of chain are entirely different from the ordinary dog snap. Such a snap itself is an example of various steels, including spring steel, and has various shielded areas. Once again, it is not enough to be able to plate percent of such a manufacturers products. It is very desirable to plate percent.

To further illustrate the tumbling characteristics of small objects, consider the plating of bolts and screws. Bolts, for example, come in a variety of sizes from very large to very small, and they may have a wide variety of head shapes. Philipshead bolts, for example, have a starshaped hole in the head of the bolt. This area must be plated completely for satisfactory commercial results. Similarly, with wood screws there is a rectangular slot for the screwdriver on the head of the screw and this must also be plated. On large bolts the threads may be fairly open and easy to reach, but on very small bolts or fine threads it is extremely difficult to penetrate to the root of the thread and deposit a uniform coating all around the thread. It may be coated with zinc, but usually the deposit in such areas is not as well consolidated as it is on more readily accessible surfaces.

Consider another case-that of small stampings. These stampings may, for example, be in the shape of small boxes. These boxes may fill up with impact medium and material during the tumbling operation and little or no plating will occur on the inside of the box. The list of problem articles could be greatly expanded but the foregoing will serve to illustrate the nature of the problems of the mechanical plater.

One of the principal difiiculties of depositing a uniform, continuous, well-consolidated coating over all of the surfaces of an article, particularly one having recessed areas, is the fact that the plating metal, for instance zinc, tends to deposit more rapidly and more thickly upon the exposed surfaces of the article being tumbled. When an efiicient system of plating activators is used, the available supply of metal can be readily deposited on the exposed surfaces, leaving little or none for the plating process to occur in the recesses because it is so slow. When an inefficient system of activators is used, which effectively slows down the plating rate to permit more time and availability of metal for a deposition in secluded and shielded areas, then the coating tends to be poorly consolidated in such recesses, whereas the use of a highly eflicient activating system would permit of better consolidation. When less efiicient promoters are used in this way, and continuous deposits of metal are laid down in shielded areas, such as thread roots, it is usually possible to scrub these out with a tooth brush. While such coatings may be serviceable for the uses intended, it is clearly an undesirable condition and one which many manufacturers will not accept. To be more successful, a mechanical plating installation should produce a large tonnage of material in the shortest possible time. Inefiicient promoters, which extend the plating time cycle, drastically cut down production from any unit and so are undesirable as well.

A principal means of dealing with the problems discussed above is by the selection of the impact material. To better understand how selection of size and shape of impact material can aid reaching recessed areas, consider small tacks which could be used as impact material to plate the interior surfaces of Philipshead bolts and to get down into the thread roots. Metal tacks used as an impact material will of themselves pick up a coating metal such as zinc, and if they are reused, will grow in size to the point where they can no longer reach the intended areas. The tacks themselves may easily be as large as the small bolts they are helping to plate, and thus a serious separation problem is created. The metal that is taken up on the tacks is not available for plating on the bolts and the economics of such a system are entirely hopeless, except perhaps in some very rare instance where the manufacturer may wish to plate tacks.

A much more practical impact medium for use with zinc plating metal consists of pie-shaped glass fragments or irregular pieces of glass. These may be very successful in plating the recessed areas, but their use can introduce major problems in the plating of articles. The principal problem from irregular or pie-shaped pieces of glass or other material used as impact media is lodgment of the irregular pieces in the work being plated. It is very difficult to insure that no lodgment will occur. For example, in Philipshead bolts it is disastrous to have any pieces of impact material caught in the recessed head, because it will not be possible to insert a screw driver. It is not sufiicient that 99 percent of the work be free of'lodgment, because with automatic machines and high industrial production, one hundred percent freedom from lodgment is the only acceptable standard. Lodgment is not the only problem associated with the use of large or irregularly shaped impact material. 'It may very easily happen that the work to be plated is smaller than the irregular impact material. This creates problems in separating the impact material from the plated work, and in some cases magnetic separation is the only possible way of accomplishing the job economically. 'A very much more desirable type of impact material consists of very fine glass beads, which have no lodgment problem and which can be pumped by a-sand pump like water. This provides a very convenient .and handy way of handling the impact medium in large industrial plants. The impact medium may be discharged by gravity from the plating barrels and after separation of the plated work, the fine beads and water can be picked up by the pump and pumped into an overhead tank where it can be returned by gravity to the barrels. Obviously, large or irregularly shaped impact material would not lend itself to the pumping technique and usually cannot be used at all.

In any operation of commercial plants which are operating two or three shifts a day, six days a week, they are bound to accumulate scrap or waste material: (in the plating of nails, for example, this could be the nail whiskers from the points of the nails). Unless the scrap is removed it will gradually accumulate in the charge until it begins to accept a substantial proportion of the available plating metal, thereby depriving the articles to be plated of such metal, and drastically lowering the efficiency. This is particularly true in the case of zinc, cadmium and other metals which plate readily. Such tramp material is difiicult to remove from large, irregula rly shaped glass pieces, but can be easily separated from title glass beads, particularly if they are pumped into a cone-bottomed tank.

Since no metallurgical operation proceeds at one hundred percent efiiciency in industrial practice, a small fraction of the coating metal powder will remain unplated at the end of the plating cycle. In the case of metals like zinc, if this metal powder is allowed to remain in the charge, it will gradually grow larger because finer metal powders will plate on the residual powder left from the preceding operation. For a while this proceeds very slowly, but after the residualpieces attain a certain size, then they reach a high degree of surface area and will pick up metal very drastically, thereby depriving the articles to be plated of metal. In extreme cases, this can result in a reduction of efficiency by as much as fifty percent, and if allowed to continue unchecked can drastically interfere-with or stop the plating itself. This means that ideally this fine metal should be removed after each cycle. If very fine glass beads are used in the impact medium and these are pumped into a cone-bottomed tank, there is suflicient residual foam to float off any unused zinc, particularly if air or solution is admitted to the bottom of the tank to create an ascending column. This cannot be done very readily with coarse or irregular glass beads, if for no other reason than they cannot readily be pumped into or fed out of such a tank. Another drawback to the use of irregularly shaped glass impact material is that if there are several different sizes used for the plating of different types of work (as there usually are) operator error will inevitably at some time, sooner or later, put the wrong impact material to the work to be plated with resulting heavy lodgment or improper plating, and the probable production of much scrap. There are other drawbacks to the use of irregular shapes, whether of glass, ceramic or other material, but enough has been said to indicate that this solution to the problem of reaching into recessed areas and plating all types of shapes which the operator is called on to plate, is an inconvenient and difficult means of solving the problem requiring a very high degree of operator know-how and care.

From all of the foregoing it will be seen that improvements in the mechanical plating art are desirable if it is to compete successfully for the proper share of the total business which its advantages as a process confer on it.

It is an object of'this invention to show how very smooth "coatings can be achieved, which are much smoother than those hitherto available. It is a further object to improve the penetration of mechanical plating coatings-into recesses of the articles to be plated. It is a further object of this invention to show how 'much better consolidation of the'coating can be achieved. It is a further object of this invention to produce thickmetallic coatings of the same quality as thin coatings and with the same degree of consolidationpIt is a further object of the invention to eliminate the orange peel effect which is normally encountered on heavy metal mechanically. deposited coatings. It will be shown that through the use of this invention, it is possible to deposit very thick metal coatings, which are. very smooth and highly lustrous, and which are so smooth that even the .experienced and trained eye can no longer distinguish between thick and thin coatings. It is a further object of this invention to produce metal coatings, such as zinc coatings, which are more suitable for subsequent dichromating because of the better smooth surfaces and better consolidation of the coating.

These and other objects which will become apparent are achieved according to the present invention by utilizing a water-insoluble aromatic organic compound in the aqueous medium of the mechanical plating process abovedescribed, said aromatic organic compound being volatile, lubricious and of low viscosity. The nature and amount of the additive can vary widely as will become more readily apparent in light of the following detailed description of the invention which includes the best mode contemplated for performing same.

What is required is a material whichwill not allow the plating metal powder to smear on the barrel sides, will not leave objectionable films on the work which will subsequently interfere with other processing operations, such as painting or dichromating. There are other considerations which it is highly desirable that any additives should satisfy. The development of excessive quantities of foam is highly objectionable. Bubbles deposited in recesses such as the slots or recesses in Philips-head screws, can prevent proper entry of the plating on the site covered by the bubble. Large quantities of foam act as flotation agents and carry into the foam a substantial proportion of the finer fraction of the glass beads. For this reason it is desirable that additives should have good defo-aming properties. It is essential that the additive could be used to excess and should not in any way poison the operation either during any particular running or accumulatingas an after effect of long continued use.

The preferred lubricious and aromatic additives of low viscosity vary widely in chemical nature and it is believed that any water-insoluble, aromatic compound having relatively low viscosity and relatively high boiling point yet relatively volatile is operable. The preferred materials, however, may be classified chemically in various manners. One preferred class materials is made up of oxygencontaining compounds including aromatic ethers, esters, alcohols, aldehydes, ketones. A preferred class may also be defined as substituted benzenes having at least the substitution indicated by the following structural formula:

wherein: R is an organic radical having the formula:

(a) -Oalkyl,

(CHz)X-C-H wherein x is an integer of from 0 to 8,

wherein R is an organic radical and wherein x is an integer of from 0 to 8,

(d) OH, or

(e) (CH2)x' C' OR3 wherein R is an organic radical and wherein x is an integer of from 0 to 8; wherein R is either an organic radical or hydrogen; and wherein R and R may together form a cyclic ether radical having the following structural formula:

Among the additives which have been tested and found to be particularly effective are:

Anisole (methylphenyl ether) Safrole (methylene ether of allyldioxybenzene) Aubepine (anisic aldehyde) Heliotropine (piperonyl aldehyde) Dihydro safrole Acetanisole (paramethoxy acetophenone) Acetophenone (methyl phenyl ketone) Propiophenone Methoxproiophenone Dimethyl acetophenone Giv Tan f (2 ethoxyethyl p-methoxy cinnamate) In general it will be noted that the preferred materials mentioned have characteristic groups substituted directly in benezene ring. These preferred groups are alkoxy, alkylene dioxy, and carbonyl linking either hydrogen, alkyl or phenyl radicals.

While all of the above listed compounds are especially effective in the practice of the invention to give smooth coatings and reach recesses they are not all useful to the same extent, for the same purposes. For example, materials containing the CH0 grouping such as aubepine produce particularly smooth zinc coatings, but they are not particularly bright or shiny. The use of aubepine has a tendency to result in a film of metal such as zinc over the sides of a rubber lined plating barrel and this detracts substantially from the plating efiiciency by removing zinc intended for the work being plated and depositing it on the barrel. For this reason aubepine is not particularly recommended for zinc or cadmium plating, but it is particularly useful in plating brass or copper, particularly if it is desired to plate using glass beads as impact material. Under the same conditions much heavier brass or copper coatings can be deposited when using aubepine in the plating operation than can be obtained when it is omitted.

On the other hand, compounds containing the methylene dioxyphenyl grouping produce very bright and shiny zinc coatings. Heliotropine produces very shiny zinc coatings, which are, however, considerably rougher than dihydrosafrole or oil of Sassafras, which produce smooth zinc coatings which are also very bright, and this particular group of materials is particularly suitable for the practice of this invention. The above mentioned zinc coatings produced in a mixture with safrole appear to have excellent lustre retention over long periods of time.

Particularly suitable for zinc and cadmium deposition are the aromatic ketones, such as acetophenone and propiophenone. These materials produce smooth, bright coatings and there is no trace of zinc build-up on the sides of the barrel, and the plating efficiencies are very high. Particularly useful for plating of brass and copper and other hard to plate metals, as well as zinc and the easy to plate metals, is acetanisole. Anisole also produces extremely bright, smooth coatings.

It is to be recognized that most of these materials have use in the perfume industry. They are high boiling point materials, and for the most part they are liquids, but they do evaporate readily. This evaporative characteristic of these materials can be extremely useful because while emulsified by agitation in an aqueous plating barrel, they help 'to produce smooth, durable and bright coatings; when the objects containing these coatings are removed into the air, the films left on the coating surfaces will evaporate very quickly and leave no residue. This means that there is no build-up on the sides of rubber-lined barrels and no deleterious interference with subsequent operations to which the coatings may be subjected, such as dichromating. From a technical point of view, materials such as acetophenone and propiophenone are very nearly ideal. On the combined basis of performance and cost, particularly useful materials are anisole, safrole, heliotropine, acetanisole, acetophenone, propiophenone.

These constitute a'preferred group of useful additives.

It has been found that phthalates have a great deal of usefulness in the practice of this invention. These materials are absolutely odor free, and are extremely inexpensive. Diethyl phthalate, for example, can be bought for about 22 cents per pound. The use of the phthalates produces very lustrous and exceptionally smooth coatings. The penetration is excellent and extremely recessed, and normally impossible areas to plate are covered effectively with a well consolidated coating. These phthalates are also useful in the plating of brass, copper and other hard to plate metals, and their use, results in enhanced depth of deposit. These phthalates, however, are not particularly evaporative, and are somewhat oily in their characteristics, particularly the higher members of the series. Among those investigated are dimethyl phthalate, di(n-butyl) phthalate, diisodecyl phthalate, diethyl hexyl phthalate, and dicapryl phthalate. The higher members of this series have very high boiling points, are quite oily, and have low vapor pressures. I find that their use tends to deposit a film of readily weldable metals, such as zinc, on the rubber surfaces of a rubber-lined tumbling barrel. This, as noted above, results in a loss of zinc to the charge and substantially lower zinc efficiencies which cannot normally be tolerated except in special circumstances. This difliculty of coating the barrel sides does not apply to brass, copper and other hard to plate metals having higher melting points and recrystallization temperatures.

It has been noted above that very small additions of these materials can be very effective. The dilution can go as low as one gram of additive to process 5 or 6 pounds of Work. Some solvent diluent vehicle spreader or other distributor for such a small amount of material is obviously desirable. Rather surprisingly, I have discovered that the selection and use of such solvents or dispersing agents results in a further improvement in the overall effect of the primary additive. There appears to be a pronounced synergistic effect. By this is meant that the use of the two materials together produces a much larger enhancement of the effect than could have been predicted from the performance of either of them used separately. The use of these solvents of which a wide choice is available, besides improving the performance in the deposition of the coating, results in the opportunity for masking odor or eliminating odor and in controlling the deposition of zinc, cadmium and similar metals on the sides of the barrel.

Among the very suitable solvents for the aromatic aldehydes, ketones, ethers and the like, which have been discussed up to now, are the fatty acid esters, particularly those of the short carbon chains, such as butyl acetate. While butyl acetate is particularly effective it has a strong, fruity odor. It is very evaporative, and will correct the tendency of some materials to leave films on the barrel sides, but it tends to be two odoriferous to use in nonvented locations. Slightly higher esters are particularly effective, for example, isobutylcaproate. A combination of isobutylcaproate and safrole, for example, has resulted in some of the smoothest and shiniest coatings.

Other solvents for these primary additives can be selected from among unsaturated fatty alcohols such as oleyl alcohol. Another particularly useful class of solvents is the glycols, for example, triethylene glycol. This is not only an excellent solvent but it is also water soluble, and will readily dissolve the phthalates described as above. When diluted with triethylene glycol, these phthalates are much improved in their performance.

Virtually all of the above listed aromatic aldehydes, ketones, ethers, and the like are soluble in one another. Therefore, it is not necessary to go to outside solvents in order to obtain the synergistic effect and the desirable combination of properties. This can be obtained by mixing two or more of the primary additives. For example, a material which has a strong tendency to film zinc on the sides of the barrel can be combined with an additive which has a good evaporation rate, and which will minimize or check entirely the deposition of zinc on the barrel. In this way it is possible to combine say propiopenone, for example, with dimethylphthalate.

In this way there is provided a very wide variety of choices in which there can be blended together various combinations of these additive reagents to lower the cost, mask odor, or prevent the build-up of films on the barrel sides. As noted, the effects can be very accumulative, and the addition of two such compounds together willexert beneficial effects to a much greater extent than could possibly be foreseen. Not only can one aldehyde be mixed with another, for example, but the mixed aldehydes can then be diluted with say triethylene glycol, for example. In this way the full potential of these additives can be realized and their disadvantages can be minimized.

While some classes of aromatic compounds will improve the lubricity of the charge, and the ability to plate into recesses and will also improve consolidation and smoothness, they appear to cause some metals such as zinc to be much darker in color than is normally the case when they are not used. The use of such materials as benzyl acetate and ethylbenzonate and benzophenone, to name some typical example, cause the zinc to be a dark, bluish color. While there may be some demand for this color in some circumstances, in the normal course of events what is required is a clear, bright, shiny color so that the use of these materials might not be indicated despite their efficacy in smoothing the coating and penetrating recesses. This is because of the ready availability of alternatives.

One more class of materials which are very useful and which have not been discussed hitherto, but which meet the requirements, are the cresols, particularly the methylated and propylated cresols such as carvacrol.

Nothing that has been said so far is intended to limit the invention to the use of a single agent such as aromatic aldehyde or ketone, and a single synergistic aid or activator such as isobutylcaproate. It is perfectly possible to add a third, fourth or fifth synergistic agent, a carrier vehicle, and a specific defoamer. In general, all of these materials are mutually soluble in one another. For example, for use in mechanical plating operations, an'additive may contain an aromatic ketone, a fatty acid ester, a silicone defoaming agent, and xylol or some other suitable solvent which is used as an over-all solubili-zer or carrier or extender. For the most part, as noted, these agents are all mutually soluble one in another, so it is not necessary to work with emulsions, although emulsions can be formulated which work very well. Even when some of the reagents are solids such as heliotropine, they may readily be dissolved in some other aldehyde such as aubepine. The substantial dilution of such reagents as dimethylphthalate in such solvents as Xylol, toluol triethylene glycol and the like, make it possible to largely overcome the previously discussed defect of depositing metal on the sides of the barrel. For the most part, these diluents or solvents are traditionally inexpensive so that a relatively substantial amount can be used without adding to the cost of the mix. Some care has to be exercised in the selection of the diluent if large quantities are to be used, so as not to interfere with the plating operation.

Experimental results, as noted before, have shown that it is possible to use ten or fifteentimes the ordinary con-- centration of materials such as acetophenone, and diluents such-as tri-ethylene glycol can be used in virtually unlimited amounts without interferring with the plating since they are all water soluble. The practical operation of the materials in various systems using the primary agents such as propiophenones singly or in combination with such synergistic agents such as butyl acetate and in more complex systems, will be illustrated and described in various examples. The examples which follow will illustrate various aspects of the process including those devoted to plating of various metals such as zinc, brass, cadmium, copper and the like.

9 EXAMPLES The following conditions were used for Examples 1 through Three pounds of spring wire hose clamps, size A-20, were well cleaned by abrasive tumbling in sand and a proprietary cleaning compound. After all scale was removed and the clamps lightly etched by the abrasive treatment, they were removed, rinsed in water, and then given a light immersion coating of copper in a standard proprietary copper sulfate bath. These were placed in a mill of about 5 quarts capacity about 6 /2 inches high and about 6 /2 inches across the flats of the hex-shaped mill. Fine glass beads, about .008 and .050 inch in size, sufficient to cover all of the voids between the clamps and to cover the surface of the charge were then added to the mill. Water was then added to the extent of 1 /2 inches over the top of the charge. Thirty grams of very fine zinc dust, having an average particle size of 3 to microns, was then added, and 35 cc. of a promoter activator was added. This activator consists of an organic acid flux, and a filming surface active detergent, in this case citric acid and a polyoxyethyleneamine. The mixture also contained a minor amout of a high molecular Weight glycol. To the above charge was added the agents described in Examples 1 through 4 that follow. More complete descriptions of the mechanical plating process to which the invention relates will be found in the above mentioned patents.

' EXAMPLE NO. 1

3 cc. of safrole were added. On opening the barrel, after one hour and fifteen minutes of operation, the clamps were beautifully coated, and the smoothness was very good, the brightness was very good, the penetration was good, there was no foam, and the overall results were excellent.

EXAMPLE NO. 2

3 cc. of acetophenone were added to the charge as described above. After one hour and fifteen minutes of operation the smoothness was noted as fair, the brightness as very good, the penetration was good, and there was slight foam.

EXAMPLE NO. 3

To the mix as described above were added 3 cc. of acetanisole. After one hour and fifteen minutes of running, the clamps were removed and it was found the smoothness was excellent, the brightness was excellent, the penetration was very good, there was no foam, the overall notation was a beautiful result.

EXAMPLE NO. 4

To the mix as described above, were added 3 cc. of propiophenone. After one hour and fifteen minutes of running, the clamps were found to be very well coated, the smoothness was very good, the brightness'was excellent, the penetration very good, the overall result excellent.

The following examples illustrate the use of two reagents; the primary and the synergistic aid.

EXAMPLE NO. 5

Purely for the purposes of comparison with Example No. 5, the run Was repeated exactly, except that 4 cc. of acetophenone were substituted for the 2 cc. of acetophenone and 2 of isobutylcaproate used in Example No. 5. All other conditions remained exactly the same. The results from this run were very good. The coating was very smooth, a good bright color, the brightness was excellent. The penetration was very good, but it was easily able to differentiate between the two results when they were compared side by side. The results from Example No. 5 were definitely smoother and better than those from Example 6, good as those were.

EXAMPLE NO. 7

The conditions for this test were exactly the same as those for Examples 5 and 6, except for the substitution of 2 cc. of butylacetate and 2 cc. of acetophenone. The clamps when removed were very beautiful, the coating was exceptionally smooth and very bright, and there was a wonderful polish in the cross over.

EXAMPLE NO. 8

Three pounds of size A-l8 springwire hose clamps as used previously were abrasively cleaned and coppered as described above. They were placed in a mill a described, with grams of zinc dust, and the additive consisted of 2 cc. of diethylphathalate, 1 cc. of acetophenone, 12 drops of a Dow Company silicone agent #200. The activator and other conditions were the same as described at the beginning of the examples, and were run for one and one-half hours. At the expiration of this time, the clamps were found to have an absolutely brilliant polish, they were relatively very smooth, there was absolutely no foam, and no odor on opening. It was possible to look through the clear liquid and see the clamps lying in the beads. The zinc etficiency was good but there was a thin skin of zinc on the barrel lining.

EXAMPLE NO. 9

For the purposes of comparison, Example No. 8 was repeated exactly, except that 3 cc. of diethylphthalate were used. On opening the barrel, brightness, smoothness, and penetration were good, but the eificiency was considerably reduced, and there was a heavy smear of zinc on the barrel sides. The clamps were not as brightly polished as in Example No. 8.

EXAMPLE NO. 10

In this test, 2 cc. of diethylphthalate plus 1 cc. of propyloleate and A: cc. of silicone 200 were used, the resulting coatings were very smooth, very bright, and there was no foam. The zinc efficiency was good, although there was a skin of zinc on the barrel side.

Three hundred parts by weight of safrole were added to 250 parts by weight of butylacetate, and 50 parts by weight of acetophenone. These ingredients were thoroughly mixed together, and a portion of this mix was used in a number of tests.

EXAMPLE NO. 11

A tumbling barrel, approximately 5 feet long, inches in diameter and divided into two compartments, each compartment capable of processing between 500 to 600 pounds of hose clamps, was used for this example. A number of different runs were made using different sizes of spring wire hose clamps, similar to those used in the preceding examples. The amounts of zinc used varied according to the size of the clamps. Approximately 550 pounds of clamps were used in each test. The promoter activator, consisting of a flux and surface active agent,

was used at the rate of 5 quarts of this agent for each 550 pounds of clamps. Suflicient glassbeads to cover the clamps were used in each test. Water was added to cover the whole charge to a depth of about 2 inches. In different tests, varying amount of the mixed safrole, butylacetate and acetophenone described above were added, in general from to 80 cc. of this mixture was used per 100 pounds of clamps. The barrel was run for minutes. On opening, each of the charges was found to be considerably smother and brighter than comparable runs made without the use of this additive. Above the cc. level of additive, there was no further improvement apparent in results, but neither was there any harmful effect noted. Penetration in the crossover of the clamps was improved in all cases. There was absolutely no interference with subsequent dichromating operations. There was no build-up on the barrel sides. The zinc efiiciency was very good. Some objection was made to the presence of odor on opening the barrel, although it was stated that the odor was pleasant. Aside from this objection, the tests were considered to be unqualified successes, resulting in a better product.

The following are some examples that relate to the plating of metals other than zinc, or to articles other than hose clamps.

EXAMPLE NO. 12

Into a small, hex-shaped laboratory tumbling barrel, identical with that described at the start of these examples, were placed two pounds of 1% x 11 roofing nails which had been abrasively cleaned and coppered. Glas beads were added to cover the charge. Twenty grams of tin powder was added, and 35 cc. of the promoter activator similar to that described at the start of these examples. 2 /2 cc. of acetanisole and 1 /2 cc. of safrole was added, the barrel was rotated for two hours. At the expiration of this period, the nails were found to be coated with a very smooth, very bright and attractive coat of tin, which was .0006 inch thick.

When articles are plated in the absence of the additives, coatings of tin metal are usually or very frequently characterized by the presence on the coating of small bumps. These are frequently referred to as tin bumps. They are believed to be caused by the rapid build-up of the coating caused by the easy platability of tin. It may be that some particles of the tin plate together before they are impacted to the coating and are thus responsible for the presence of these small, inconspicuous, but none theless unattractive, tin bumps. The use of acetanisole and safrole in combination entirely eliminated the presence of tin bumps, and the coating was remarkably smooth and uniform.

EXAMPLE NO. 13

One pound of roofing nails, 1% x 11 in size, were added to a hex-shaped laboratory barrel, similar to that described previously. To this were added glass beads sulficiently to cover the nails, so that the barrel was approximately one-third full of nails and beads. Water to cover to a depth of two inches over the top of the charge was added.- To this was added cc. of concentrated sulphuric acid and 2 grams of sulphosalicylic acid, 6 grams of polyoxyethyleneamine and 50 grams of 70-30 fine brass powder. To this charge was added 4 cc. of acetanisole. Themill rotated for three hours. At the expiration of this test, the nails were found to be coated with a very pretty brass coating, which was smooth and shiny. The average coating thickness was .0006 inch. The brass was an excellent yellow color.

. To illustrate the usefulness of the multicomponent systems, the following mix was prepared:

50 cc. butyl stearate 30 cc. carvacr ol 20 cc. aubepine 1 gram heliotropine All of these were dissolved in 100 cc. of a mineral spirit containing a minor amount of silicone defoamer.

EXAMPLE NO.- 14

Some woven wire chain, one and one half pounds in weight, was added to the small hex-shaped barrel, similar to those used above. To this was added glass beads to cover, 10 grams of Zinc dust, 40 cc. of the promoter activator, similar to that described above, and 100 drops from a medicine dropper of the multicomponent additive just EXAMPLE NO. 15

Example 14 was repeated, except that one and one-half pounds of sash chain was substituted for the woven. wire chain. The chain was found to be completely coated with zinc, including the recessed areas on the inner surfaces of the sash chain. This. type ofrecess is very small and hard to get into, and for the most part is very difficult to plate using conventional means.

From the foregoing, it should be apparent that the invention resides in the use of certain aromatic organic additives which have been found to improve the mechanical plating processes described by providing greater penetration. While a broad class of water-insoluble aromatic organic additives is described, the most useful materials appear to be non-acidic, lubricious, high boiling, volatile or non-persistent and of low viscosity, By lubricious" is meant non-sticky. Water insoluble is used in its accepted sense as including very slightly soluble materials.

The term volatile as used herein is intended to mean non-persistent. That is, the materials will have measurable vapor pressure at relatively low temperature. Preferred materials have a vapor pressure of at least 5 or 10 mm. Hg at 100 F., although less volatile materials can be used.

The term low viscosity as used herein is intended to mean, light, free-flowing materials as opposed to heavy or waxy materials. The viscosity of the preferred ma-. terials is generally below 50 or 100 cps. at temperatures of up to about 100 F. although more viscous materials may be used. Still more preferably, the viscosity of the materials is below about 20 cps. at room temperature.

The mechanical plating process, together with full description of suitable filming agents and fluxes which comprise the plating promoter described, are all included in the patents mentioned in the opening paragraph of the specification. It will be known by those skilled in the artv that various fluxes an-d filming agents as well asdefoamers and the like arev known to be useful in the process and can be used in the basic mechanical plating processand in widely. varying amounts. It will also be known that various impact materials, including the articles to be plated, may be used in the basic process. In short, the present invention is generally applicable to the known aqueous mechanical plating process. 1

As mentioned above, the present additive can be used in very small amounts but very large amounts do not cause any difficulty. Accordingly, there does not appear to be any requirement to limit the amount of additive to any minimum or maximum values .as some improvement in penetration and smoothness is obtained with minuscule additions. As mentioned, as little as 1 gram of additive to 6 pounds of work, or 0.05% by weight, additive has been found quite effective. In general, however, it can be said that for a normal charge of from l00parts to 2500 parts of work, from 0.1 part to 50 or 100 parts of the water insoluble additive can be effectively used. On this basis, the amount of additive could vary from 0.005 to 100 wt. percent, based on the amount of work to be plated.

On the same basis of from 100 to 2500 parts of work, a charge would ordinarily include from 5 to 300 parts of metal plating particles, from 500 to 3000 parts of water, and from 5 to 200 parts of promoter which itself is conveniently water, 10% filming agent and 25% flux.

13 The impact media, if not the object to be plated, can be used in amounts of from 400 to 3000 parts. Accordingly, the amount of additive used according to the invention can be based on the work, or on the charge, or any of the components.

What is claimed is:

1. In a method of applying metallic coatings to metallic objects by subjecting finely divided metallic particles to mechanical energy in an aqueous medium to flatten and cold weld the particles to the metallic object to thereby build up a continuous adherent metallic coating on said metal object, the improvement wherein a water-insoluble oxygen-substituted lubricious aromatic organic compound additive is provided in said medium to improve said plating process, said additive being present in an amount of from 0.005 to 100 percent, by weight, based on the weight of said metallic particles and having a vapor pressure of at least mm. Hg at 100 F. and a viscosity of less than 100 cps. at 100 F.

2. An improved method according to claim 1 wherein the additive comprises at least orie substituted benzene having at least the substitution indicated by the following structural formula:

wherein:

R is an organic radical having the formula:

(a) -O alkyl,

wherein x is an integer of from 0 to 8,

wherein R is an organic radical and wherein x is an integer of from 0 to 8,

(d) OH, or

wherein R is an organic radical and .wherem x 18 an integer of from 0 to 8; wherein R is either an organic radical or hydrogen; and

wherein R and R may together form a cyclic ether radical having the following structural formula:

3. An improved method according to claim 1 wherein the additive comprises at least one compound selected from the group consisting of aromatic ethers, aromatic ketones, aromatic aldehydes, aromatic esters, and aromatic alcohols.

4. An improved method according to claim 3 wherein the additive comprises at least one aromatic ether.

5. An improved method according to claim 4, wherein the ether is selected from the group consisting of anisole, safrole, isosafrole, dihydros-afrole, aubepine, heliotropine, acetanisole, methoxypropiophenone, 2 ethoxyethyl p-methoxy cinnamate and mixtures thereof.

6. An improved method according to claim 3 wherein the additive comprises at least one aromatic ketone.

7. An improved method according to claim 6 wherein the aromatic ketone is selected from the group consisting of acetophenone, dimethylacetophenone, propiophenone, benzophenone, and mixtures thereof.

8. An improved method according to claim 3 wherein the additive comprises at least one phthalic acid ester.

9. An improved method according to claim 8 wherein the ester is selected from the group consisting of diethyl phthalate, dimethyl phthalate, di (n-butyl) phthalate, diis'odecyl phthalate, diethyl hexyl phthalate, dicapryl phthalate and mixtures thereof.

10. An improved method according to claim 3 wherein the additive comprises at least one cresol.

11. An improved method according to claim 10 wherein the cresol is carvacrol.

12'. An improved method according to claim 3 wherein the additive comprises at least one aromatic aldehyde.

References Cited UNITED STATES PATENTS Re. 23,861 8/1954 Clayton 117109 2,461,809 2/1949 Chester et a1. 2,689,808 9/1954 Clayton 117109 X 3,023,127 2/1962 Clayton 117--131 X 3,132,043 5/1964 Clayton 117109 3,201,273 8/1965 Maker et a1. 1l7131 X 3,328,197 6/1967 Simon 117-109 FOREIGN PATENTS 667,215 7/ 1963 Canada.

ALFRED L. LEAVITT, Primary Examiner THOMAS E. BOKAN, Assistant Examiner US. Cl. X.R. 

